The purpose of the assignment is to develop a simulation of a robot in a 2-dimensional environment, using the CoppeliaSim simulator. The adopted robot corresponds to the Pioneer P3-DX.
The package is composed of four nodes and three servers. The nodes are go_to_point, user_interface, position_service, state_machine. The servers are Command, RandomPosition and Position.
As already said, the node go_to_point implements a server: when it is called it receives a request to reach a point with a given orientation. On top, it implements the algorithm to control the robot. The node user_interface reads the inputs given by the user: depending on the input received, it can recall the go_to_point service. The node position_service implements a server that replies as response a feasible pose of the robot: since the considered space has two dimensions, the client that requests this service receives an x-coordinate, a y-coordinate and an orientation theta, in which the point (x, y) and the orientation are chosen among a certain range of values. The node state_machine implements the server for the user_interface client. On top, it also implements a client for both the position_server and the go_to_point.
Regarding the simulation, it is possible to find the "prova_scene.ttt" scene, that implements the robot simulation in CoppeliaSim. Referring to the associated script, it is possible to notice a publisher to the /odom topic, on which the current position of the robot is published. The node go_to_point subscribes to this topic. A subscriber to the /cmd_vel topic is declared, topic on which it is possible to retrieve the velocities of the two wheels of the robot: as soon as new data are available on the /cmd_vel topic, there is a "velocity" function that sets, using the differential form, the velocities of the wheels of the used model.
Verify that you have installed ROS Noetic. Create a ROS Workspace and clone this ROS package inside it
git clone -b main https://github.com/RiccardoZuppetti/RT2-Assignment1.git rt2_assignment1
Then build the workspace using the catkin_make command.
Modify the .bashrc file, using the command gedit ~/.bashrc, sourcing the ROS environment, the ROS workspace and exporting the correct directory of CoppeliaSim_Edu_V4_2_0_Ubuntu20_04.
To run this project it is necessary to open two terminals.
In the first terminal move to the created ROS workspace and digit
roslaunch rt2_assignment1 sim.launch
In the second terminal move to the CoppeliaSim_Edu_V4_2_0_Ubuntu20_04 folder and digit
./coppeliaSim.sh
Once CoppeliaSim started the "prova_scene.ttt" must be opened, which is inside the package cloned. Then, the CoppeliaSim simulation must be booted. When the simulation has started, it is possible to move the robot pressing (in the first terminal opened) the "1" key: in this way, the robot will move towards a random position and orientation. To stop the robot movement it is necessary to press the "0" key.
Once the simulation is booted, the robot is positioned in the (0, 0) point, with a 0 orientation and a null velocity: the robot remains in this state until the user starts the robot motion. When the motion has been started, the robot reaches a random position in the environment, with a random orientation. If the user wants to stop the robot motion, the robot will stop as soon as the goal position has been reached.
Both nodes go_to_point and user_interface are implemented in Python, and so it is important to make the associated scripts executable. The nodes position_service and state_machine are implemented in C++. Concerning the architecture used, the state_machine node controls the entire execution, since it can receive inputs from the user_interface, can send a request for a random position to the position_service, and finally can invoke the go_to_point service in order to reach this random position.